Soil organic carbon pool under selected tree plantations in the Southern Western Ghats of Kerala, India

Abstract

Soil organic carbon (SOC) is the most important indicator of soil quality and land-use sustainability. We evaluated the SOC pool and selected physico-chemical soil variables after conversion of native forest to monoculture tree plantations (teak, eucalypts and rubber) in the Southern Western Ghats region of Kollam district, Kerala, India. Soil samples were collected up to a depth of 50 cm in five depth increments from six locations each from the four selected land-use systems. Soil analyses were carried out as per standard methods. Average SOC concentration ranged from 41.89 to 54.09 g kg⁻¹ (0–10 cm), and found decreased with depth up to 30.11 to 32.98 g kg ⁻¹ (40–50 cm). The highest SOC pool (0–50 cm) was observed under natural forest (225.34 t ha⁻¹), followed by rubber (203.48 t ha⁻¹), eucalypts (196.21 t ha⁻¹) and teak plantation (194.61 t ha⁻¹). Similarly, the SOC mitigation potential (carbon equivalent to CO₂) decreased in the order natural forest > rubber > eucalypts > teak plantation. The SOC concentration showed significant variation between natural forest and tree plantations. Principal component analysis (PCA) was used to determine the major factors and trends to illustrate the variability in the data. PCA results suggest that higher SOC contents and its fractions were closely linked to the surface layers (0–20 cm) of soils under all treatments. Overall conclusion from this investigation is that SOC levels are strongly influenced by the prevailing land-use systems and found to decrease after conversion from natural vegetation to monoculture tree plantations. The information presented herein on the depth distribution of the SOC fractions and trends in aggregate carbon content may improve our knowledge and help in framing soil carbon prediction models in this region.